A printing press includes a plurality of printing stations. Each printing station prints a respective color image on a common area on the web. The color image exhibits a respective color. Thus, the printing press forms a printed image on the web. The color of each color image may be a process color in a color gamut such as Cyan Yellow, Magenta and Black (i.e., CYMK) or Red, Green and Blue (i.e., RGB) or a pantone color. A pantone color is a specially manufactured color that cannot be accurately produced from a combination of basic process colors. For the image to be printed correctly, the printing stations in the printing press must be in register with each other (i.e., each station prints the respective color image thereof at the respective location associated therewith), such that the images to be printed shall all be printed in the correct relative positions in the common area on the web.
U.S. Pat. No. 5,812,705 to Wang et al, entitled “Device for automatically aligning a production copy image with a reference copy image in a printing press control system”, directs to a system which includes a 4 CCD camera coupled with a computer. The 4 CCD camera is operative to acquire an image of reference print in Red, Green, Blue and Infrared. This reference print serves as a hard proof of the live print. The reference image is converted into a monochrome image. Four object models are identified at each quadrant of the reference image. These object models are features in the image (i.e., transitions from dark to light) within a quadrant.
During the registration, the 4 CCD camera acquires a live image of the print. The live image is converted into a monochrome image. The computer then looks for a model within the models search region. Each potential find is given a score indicating the likelihood that the model was actually found. When the computer declares that the model was found (i.e., according to the score thereof), the computer defines a transfer function which maps the position of the found model to the position of the model found in the reference image.
U.S. Pat. No. 6,129,015 to Dewey, entitled “Method and apparatus for registering color in a printing press” directs to a method including the steps of identifying an area of the desired image that is intended to be printed in black, and forming registration images on the plate cylinders of the printing stations. The registration images are positioned on the plate cylinders such that, during subsequent printing operations, they will produce color registration marks that cooperate to print a process black registration mark on the web in the identified area (i.e., when the printing stations are in registration). The publication to Dewey further directs to a method comprising the steps of passing a web through the plurality of printing stations and printing a process black registration mark on the web. Furthermore, a black ink image on the web, adjacent to the process black registration mark, is printed. Thereafter, the process black registration mark and the black ink image are examined and an error signal is generated when the process black registration mark is not in desired registration relative to the black ink image. It is noted that the term ‘registration marks’ in the publication to Dewey refers to part of the image that is printed in process black and not in black.
U.S. Pat. No. 5,689,425 to Sainio, entitled “Color registration system for a printing press”, directs to a system for generating a signal representing a color registration offset between at least two colors of an image, printed on a web. The system includes a memory which stores two reference arrays of digital data representative of the colors of at least a portion of the image. An imaging device is arranged in optical communication with the web, to produce analog signals representing the colors of the portion of the image. The system also includes a converter circuit which converts the analog signals to a color array of digital data. These arrays are stored in memory. The system further includes a processing circuit in communication with the converter circuit and the memory. For each color, the processing circuit, phase correlates the reference array of one color with the on-press array of that same color and phase, and determines a registration offset between the colors. The processing circuit produces a signal representing the registration offset between the colors.
PCT Publication WO 2006/081950, to Loddenkoetter et al, entitled “Registering Method”, directs to a method for registering a rotary press with a plurality of inking mechanisms. According to the method directed to by Loddenkoetter et al, a longitudinal screen mark and a horizontal screen mark are mounted at a fixed position on the frame of the rotary press in front of an optical sensor. These screen marks represent the required position of the printed image. Each printing station, in the rotary printing, prints the respective image thereof. An optical sensor acquires an image of the printed images. The position of the printed images relative to the screen marks are apparent on the image acquired by the optical sensor. An operator adjusts the location of the printed image accordingly, until the printed images are flush with the screen mark.
German patent application DE19855177, to Krumpelmann, entitled “Method for the Automatic Adjustment of Circumference and Side Registers of Press Cylinders”, directs to a method for adjusting individual printing units in a printing press. Each printing unit prints a print image. The printing press prints superimposed print images. The method includes the steps of selecting a print image printed by a printing unit as a reference image, recording with a camera the superimposed print images and comparing the actual position of the print images with respect to each other, and with respect to the desired position of each print image. The method further includes the steps of generating correcting signals for adjusting the press cylinders circumferential or side registers and actuating motors of the press cylinders according to the generated correcting signals. The reference print image may be the first print image or one that exhibits simple composition.